Why is sex hurting?

So I am not new to the same game. I have had sex before and I am in my mid 20s. I started dating this guy several months ago and we recently started having sex. He isnt huge he is average but every time we have sex it hurts. It feels like his dick is running into my cervix or something. Like it feels like it hits something up there. This never happened with my ex who was bigger. Any ideas?